A fog machine is a device that emits a stream or puff of visible vapor or fog for theatrical or similar purposes. The effect can be enhanced by projecting light through the emitted fog to provide a dramatic visual effect on stage, in a dance club, etc. A fog machine operates by pumping a non-toxic fog fluid, such as glycol, glycerine, or a water-based mixture thereof, into an airstream and past a heating element. The airstream is typically provided by a fan. The heating element causes the fluid to vaporize, producing a visible vapor or fog.
Fog machines are typically portable but not especially compact, generally having a boxy shape with a size on the order of that of a small suitcase or briefcase and weighing on the order of 5-10 pounds (2.25-4.5 kilograms) or more. Most fog machines are powered by utility power, i.e., they must be plugged into a wall outlet, portable generator or similar source of utility-level power. Accordingly, fog machines are typically brought to an unobtrusive location in a corner of a theater stage or other location where a performance or other activity is to take place, left in place throughout the activity, and used at times during the activity to produce fog. Compact, battery-powered fog machines have been developed, but remain uneconomical due to complex, specialized parts.